Waving SG's when hops are already in front lines?

So guys I'm about to attack someone with 1000 hops, 500 swords, 250 SC's and 120 SG's and I want to wave my SG's but I don't understand if they will even go to battlefield when I wave them because I read in many forum posts that Hops has always priority in front lines. So what's the point of waving then if my hops stays in front lines until they die? I clearly don't understand something completely. Please enlighten me!

They won't take join the battle indeed, unless you send them alone as frontline (no hops, or at least not enough to fill the frontline). No point to wave them in that situation.

If you had, say, 600 SGs, you could try to wave 300 by 300 for example, leaving the hops behind until you can't wave the SGs due to casualties. Not saying this is necessarily the best choice, but it could be attempted.
120 don't sound like a huge lot, although that depend on the field size. On a small field (against troops in defense not exceeding the garrison limits), you could go with SG waves. On the big battlefield, splitting your 120 doesn't seem advisable.

Thank you! It was impossible to find this kind of information in web.
Still I'm not sure, what's the best SG unit amount that I should wave and why is it the best ? Before I was thinking that I need to wave 70 SG units per round because that's the max. amount of SG's that can be in front line but after you mentioned those '300' i'm not sure anymore, please explain. Btw. much appreciated.

Waving SGs is good only if opponent has no mortars/cats or forged bat. rams.....so if he has no 3rd line or unforged bat. rams it is worth it....
If your field fits 70 SGs...then that is how many you need to send each round and recall them as soon as they arrive and you see the option to flag them, when you do send 70 more fresh ones, when they arrive flag them and send 70 more...rinse and repeat...Return time on island is 1h15min, that is 5 rounds + 1 extra you will need a total of 70x6=420 SGs to wave...and make them 500 in case of casualties or in case you forget to recall etc....

What was said above is correct...in a sense. Steam giants are usually only good against an unforged army fielding battering rams. So, you usually won't fight with steam giants.

This isn't to say that steam giants are useless or that you shouldn't have some if your account is large enough to support a full and proper army. I always keep a few hundred steam giants in one of my wave points just in case the rare occasion that they are needed arises. Yes, the SGs cost a bit of gold just to keep around for that rare occasion but I really don't like losing a battle to anyone...at least not by damage ratios.

The only time that steam giants are really worth it, and the reason I always keep some in a wave point, is if both me and the person(people) I am fighting are evenly matched (forges running, both waving properly, and the same basic military set up). In this case, I send in the steam giants. I'm not giving you the exact numbers as it took me months and even years of trial and error to get maximum damage given and minimum damage received down to a science and I'm not keen on giving out hard won info for nothing.

But the basic idea is this...when you're evenly matched (50/50 damage ratio), send in a full line of steam giants, withdraw the hops you have on the field, and start waving in 150 hoplites every round (just like you would wave in flames in a naval battle). This will give you a 55/45 advantage on damage ratio even if everything else is perfectly even (forges, waving, and other troop types).